Light source



May 16, 1933. E. D. WILSON LIGHT SOURCE Filed April 23, 1930 I Phase Ski tiny Del/ice.

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Amp/War Loud speaker INVENTOR Ear/D. 14/275077.

ATT'oRNEY Patented May 16, 1933 UNITED STATES- PATENT OFFICE EARL D. WILSON, OF W'ILKINSIBUBG, PENNSYLVANIA, ASSIGNOB '10 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA LIGHT SOURCE Application filed April 88,

This invention relates to light sources and especially to an alternating-current lamp adapted to excite a light-sensitive device.

An object of my invention is to use an altermating-current lamp in which the total luminous flux from the lamp is not affected 'by the alternations of the current through the filament. More specifically, it is an object of the invention to utilize a lamp having a double filament, in combination with means to shift the phase of the current through one of the filaments 90 from the phase of that through the other filament, so that the integrated flux from the lamp will not be appreciably affected when either current passes through zero during its cycle. Furthermore, it is intended to use this particular type of lamp in combination with a photo-tube operating, for example, a loud speaker, so that the loudspeaker will not reproduce a 120-cycle hum caused by the alternations of the current through the light source.

It has heretofore been the practice, in systems using a light source for actuating a sensitive light-responsive device, to use direct current, either from a direct-current source or from rectified alternating current source. This has been necessary because the light sensitive device is more sensitive to the effects of the alternations of the current through the filament than is the normal eye. Alternating current, passing through the ordinary 60- cycle house lamp, for instance, passes through a zero phase twice during each cycle. The result is that the light tends to become dim as the current changes from the one to the other direction. The normal eye however, is not adapted to perceive this quick change when a 60-cycle current is used, because of the familiar phenomenon of persistence of vision. Photo-tubes, however, respond instantaneously to variations in light flux, so that they readily detect changes which the eye would not perceive. This instantaneous response of the photo-tube has hitherto prevented the use of unmodified alternating current as a means of filament incandescence. Accordingly, battery operation or a system of rectified alternating current has heretofore been used.

1930. Serial No. 448,518.

' A battery system is cumbersome and troublesome and a direct current produced by rectification has not always been perfectly .Fig. 2 is a cross-sectional view through a preferred type of light source, according to the invention;

Fig. 3 is a diagrammatic view of a phaseshifting device, of one type.

A more or less common type of light-sensitive device is disclosed in Fig. 1; in which a photo-tube 10 is connected to an amplifier 11 for controlling the operation of the loudspeaker 12. The film 13 has thereon, preferably at one edge, a sound track, either of the variable-area or variable-density type. A source of light is generally concentrated on the sound track 14 on the film and the passage of the light thereth rough energizes the phototube 10 and, accordingly, the loud-speaker. As the transmitted light varies in intensity, the tones produced by the loud-speaker also vary in accordance therewith, and musical sounds or speech are thus produced by the loud-speaker.

As the photo-tube 10 is instantaneous in response, it is apparent that an unfaltering source of light should be used for the illumination of the light-sensitive device 10. This has heretofore required direct current for the filament of the lamp because unmodified alternating current produced a fluctuation in brilliance that could afl'ect the operation of the photo-tube 10. A lamp constructed according to this invention, a preferred type of which is disclosed inFig. 2, permits of the use of unmodified commercial alternating current through its filaments.

This lamp has the usual bulb 15 supported on a base 16 and has an interior 17 either evacuated or filled with an inert gas. Preferably, three conductors 18,19 and 20 extend, throu h the glass seal 21, to the upper portion of t e tube. A double filament is attached to one of the conductors, for example, 18, and has its other two ends fastened to the conductors 19 and 20. This double filament may, of course, be of one strip such as tungsten, with its center portion 22 fastened to the conductor 18 and having. two ends 23 and 24 intertwined or twisted about each other and connected at 25 and 26 to the conductors 20 and 19. The intermediate sections of the two filaments are, of course, out of contact .with each other. The outer ends of the conductors 18, 19 and 20 have suitable prongs 27, 28 and 29 attached thereto for insertion in a supporting socket.

The specific form of the filaments is particularly adapted for illumination of the sound track 14 on the film. Each of these horizontally aligned filaments has the shape of a helix, and the projection of this shape when incandescent on the sound track itself is substantially that of a. rectan 1e. Any slight irregularity on the edges 0% the projection of the filament upon the film does not affect the operation, as this irregularity will fall just outside the sound track. The rectangle of light concentrated on the sound track is projected from within a space defined by the points 40, 41, 42 and 43. The space within these points is so occupied by the intertwined double helix of the filaments that the light flux from either filament will supply the complete illumination focused on the sound track in the shape ofa rectangle. Accordingly, if the fluctuations in light intensity from one filament can be directly compensated by an opposite fluctuation in light intensity from the other filament, the intensity of illumination of the sound track will be constant. This constant illumination is obtained by changing the phase of the current through one of filaments 90 from that of the other filament.

In Fig. 1, the two filaments 23 and 24 are diagrammatically illustrated at the left of the figure in a separate position, for the sake of clearness. The filaments preferably have the alternating-current connections attached to a source of alternating current 30. A transformer is preferably inserted between the source of alternating current and the two filaments, as disclosedin the figure. This transformer has primary coils 31 and secondary coils 32 and 33 for the filaments 23 and 24, respectively. It is preferred, however, to insert a phase-shifting device 34 between one of the secondary coils, such as 32, and its filament to shift by 90 the phase of the current through the filament 23. This phaseshifting device ma be of any suitable type, either electro-mec anical or purely electrical.

In Fig. 3, is an example of an electrical means or filter applied to both connections to the filaments 23 and 24. In this case, however, it would not be necessary to have the two secondary coils 32 and 33, as they could be replaced by a single secondary coil. In Fig. 3, thevalue of inductance 35, preferably in the shape of a choke coil, and a resistance 36, in series with the filament 23, in combination with a capacitance 37, in series with the filament 24, is chosen so that the phase of the current in the two filaments differs by 90. Other standard forms of phase-shifting devices could be'used for large filament currents.

The filaments 23 and 24 have their radiant flux concentrated by a lens system, represent ed by the lens 38, upon the sound track 14 of the film 13. While a single lens is shown in the figure, this lens represents the usual optical system invwhich a plurality of lenses are used for accurately and carefully focusing the light at the desired place on the film.

In operation of the device, the filaments 23 and 24 are excited to incandescence by the alternating current passing therethrough. The alternating current, however, passes through a zero phase in each filament twice during the cycle. If the usual (SO-cycle commercial current were used, the filaments would ordinarily flicker 120 times a second because of the alternations of the current. While this could not be perceived by the normal eye, it would affect the operation of the sensitive photo-tube 10 and result in a 120-cycle hum being produced in the loudspeaker 12. However, in this invention the phase of the current through one filament is 90 out of phase with the current through the other, so that, when the current through one filament is passing through zero phase, the other filament is at its highest temperature. Accordingly, the lamp supplies a continual brilliant illumination that is not affected by the zero phase of the alternating current in each filament. As the illumination of the light-sensitive device 10 is not affected by the alternations of the current, there will be no bum in the loud-speaker because of the use of alternating current in the light source.

It is obvious that modifications of the invention, may be made, and that the invention may also be applied to other uses than that disclosed in Fig. 1. The shape and connections of the filament in the bifilar lamp of Fig. 2 may be varied. Furthermore, the invention is not limited to shifting the phase exactly 90 although that degree of shift is preferred. The invention may also be applied to other uses than that of controlling the loud-speaker by means of light through a film. It might, for example, be

. reproducing them.

My invention therefore, is not to be. restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. Apparatus for photographically recording sound on a film or for reproducing sound from a film record comprising a plurality of overlapping light sources, means for supplying to said sources alternating currents differing in phase, and means for projecting the combined light from said sources onto the film.

2. Apparatus for photographically recording sound on a film or for reproducing sound from a film record comprising a plurality of v overlapping light sources, means for directing onto said film record the light from said sources, a photo-electric cell arranged to receive said light modulated by the record, and means for supplying alternating current to said light sources, the currents in the respective sources having a phase displacement relative to each other.

3. Apparatus for photographically recording sound on a film or for reproducing sound from a film record comprising a plurality of overlapping light sources, means for directing onto said film record the combined light from said sources, a photo-electric cell arranged to receive said light modulated by the record, and means for supplying alternating'currents of differing phase to the respective sources for energizing the same.

4. Apparatus for photographically recording sound on a film or for reproducing sound from a film record comprising an alternating current lamp having a plurality of intertwined filaments, means for supplying to the respective filaments currents having a predetermined relative displacement, means for focusing the combined light from said intertwined filaments in a narrow band on the film and a photo-electric cell arranged behind the film to receive said combined light I as modulated by the record.

In testimony whereof, I have hereunto subscribed my name this 18th day of April EARL 1). WILSON. 

